Solvent extraction of oil



May 15, 1956 R. E. MANLEY SOLVENT EXTRACTION OF OIL FiledV oct. 11, 1951 IN V EN TOR. f/ E y TONE' YS' United States Patent O soLvENT EXrnAcrIoN or on.

Robert E. Manley, Yonkers, N. Y., assigner to The Texas Company, New York, N. Y., a corporation of Delaware Application October 11, 1951, Serial No. 250,844

Claims. (Cl. 196--14.26)

The present invention relates to the solvent extraction of liquid petroleum oils containing extract fractions coboiling with the solvent, namely hydrocarbon constituents having true boiling points approximating and below the boiling point range of the solvent employed.

'I'he present invention is particularly applicable, therefore to extraction of hydrocarbon oils by a solvent such as furfural wherein a feed oil, such as a middle distillate, kerosine, a low boiling gas oil, or a fluid catalytic cracking cycle oil is treated with a solvent effective to form extract and raffinate phases respectively.

The raffinate phase comprises non-aromatic or relatively insoluble constituents of the oil, together with a small proportion of the solvent. The extract comprises the relatively aromatic and more soluble constituents of the oil dissolved in the main body of solvent. The extract and rainate phases are in turn separately subjected to fractional distillation to strip the solvent substantially or completely from the oil. The resulting distillates, either combined or separate, are condensed and permitted to settle with the formation of oil-rich, water-rich, and solvent-rich layers respectively. Liquid streams are continuously withdrawn from these separate liquid layers for further treatment.

In accordance with the present invention, the solventrich stream decanted from the solvent-rich condensate layer is treated for the separation and removal of dissolved light oils by subjecting it to extraction with a relatively high molecular weight parafnic oil having a high solvent aflinity for relatively light hydrocarbon fractions with true boiling points approximating that of the solvent and below. The heavy parainic oil, being relatively insoluble in the solvent, selectively extracts and removes from the solventrich stream the co-boiling and lighter fractions which are otherwise only diicultly removable by distillation.

Furfural, for example, boils at about 323 F. and therefore where furfural is repeatedly reused to extract light oils it tends to build up in the co-boiling aromatic hydrocarbons. In `such case, the recovered solvent-rich layer is therefore extracted with a parainic oil having an ASTM initial boiling point not below 580 F. and preferably at least about 620 F., such, for example, asy a solvent refined light neutral oil, or a ranate from fluid catalytic cracking unit decanter oil.

As a result of thus contacting the solvent condensate with the higher boiling parainic oil, dissolved co-boiling aromatics or other hydrocarbons relatively soluble in the solvent are separated therefrom, yielding as bottoms a solvent stream low in co-boiling and lighter hydrocarbons. Therefore, the resulting solvent, low in dissolved light hydrocarbons may be continuously recycled for the extraction of additional feed oil, either with or without intervening additional purification or drying as desired.

The relatively high molecular weight paranic oil containing the coboiling hydrocarbons extracted from the solvent, is continuously subjected to water Washing to scrub out accompanying furfural and thereafter regenerated by steam stripping the light co-boiling hydrocarbon fractions. As a result, the regenerated high molecular Weight paranic fraction may be recycled continuously for the extractive puriication of the furfural-rich condensate stream.

Advantageously, the relatively high molecular Weight paraffinic oil from the treatment of the solvent-rich stream passes to the water washing step together with the oilrich condensate to effect simultaneous recovery of entrained solvent.

The water-rich condensate from the stripped primary extract and rallinate distillates, together with the Wash water from water scrubbing the oil streams, may be passed to a fractionation system for the recovery of solvent and the elimination of water. Provision may be made for recycling a portion of the water-rich layer as reflux to the rafnate or extract phase fractionating zone or for recycling a portion of the oil-rich condensate layer to either of the fractionating zones to work off this stream in the railinate and extract oil products.

The primary advantage of the present invention is based upon the fact that the recycle solvent brought into contact with the charge oil is thus continuously low in hydrocarbons, having a true boiling point approximating or below that of the solvent, as is comprehended herein by the term co-boiling light hydrocarbons. In particular, the recycle solvent is low in dissolved co-boling aromatics. Therefore, its extractive capacity is correspondingly enhanced, particularly as regards the light aromatic fractions.

For example, the ordinary tendency toward build-up of co-boiling light aromatic oils results in an equilibrium concentration of these constituents in the solvent such that the solvent capacity for these oils is materially impaired.

In accordance with the present invention, however, the continuous separation of light aromatic fractions from the fractionated solvent by means of a relatively high molecular weight paranic oil results in a recycle solvent low in objectionable co-boiling fractions, thereby improving the extraction, extending the eiect of furfural rening to the lower boiling products and permitting recovery of aromatics boiling in a range corresponding to that of the solvent.

In order to describe the invention morein detail, reference is now made to the accompanying drawing comprising a flow diagram of the process as applied to the treatment of a uid catalytic cracking cycle gas oil having an ASTM initial boiling point of 420 F. and an end point of 620 F.

As indicated in the drawing, the feed oil is introduced from a source, not shown, through pipe 10, after such temperature adjustment as may be necessary, to the lower portion of charge oil extraction tower 11.

The feed oil rises through the packing of the tower 11 countercurrently to a stream of solvent liquid introduced to the upper portion of the tower through pipe 12, to which reference will be made later. The solvent comprises furfural which may contain water or may be substantially free from water as will hereinafter appear. The solvent is introduced to the tower in the proportion of about one volume of solvent to two volumes of feed oil. The temperatures of the entering streams of oil and solvent are regulated so that the temperature at the bottom of the tower 11 is maintained at about 80-100" F. while the temperature at the top is around ll0-l50`F.

Under these conditions, extract and raffinate phases form. The raiiinate phase comprises oil of relatively high cetane number, with a small portion of the solvent liquid, and is continuously removed from the tower through pipe 13, and introduced into raffinate oil stripper 14. In the ratlinate oil stripper 14 the solvent is distilled from the rafiinate oil. The stripper may be provided ducted to an extract oil stripper or fractionating tower '17 which operates in a manner similar to that of raffinate -oil stripping tower 14.

With furfural as the extraction solvent, it is advantageous to maintain the temperature at the top of the strippers 14 and 17 Within the range of about 3D0-330 F. The temperature at the bottom of the strippers is preferably maintained suiciently high to distill all, or

substantially all, of the solvent from the oil. Therefore,

4solvent-free ra'inate oil is discharged through pipe 18 land solvent-free extract oil is delivered through pipe 19.

-The distillates from the raffinate oil and extract strippers, comprising a mixture of furfural, oil vapor, and usually water vapor, pass overhead from the strippers through pipe and cooler 21 where they are con- Adensed and passed to a settling chamber or decanter 23. .In the settling chamber the condensate separates into `oil-rich, water-rich and solvent-rich layers.

Preferably the settling is effected in the presence of a water layer to facilitate separation of the solvent from the bulk of Vthe oil.

The solvent-rich layer is continuously drawn off from l, the decanter 23 through pipe 24.

With a cycle gas oil feed stock as indicated above and performing the extraction with about 55 volumes of recycled furfural per 100 volumes of feed oil, the oil content of the solvent-rich stream in pipe 24 will "reach an equilibrium amounting to about 25 by vol- 'ume of aromatic oil of the following characteristics:

l API gravity 32.

lBP 180 F. 50% 290 F. EP 435 F.

To avoid recycling this contaminated solvent to the vcharge oil extraction, the solvent-rich stream therefore passes into a furfural extraction tower 25 where it moves downwardly through the packing of the tower countercurrently to the stream of relatively high boiling parafnic oil introduced to the lower portion of the tower 25 through pipe 27 to which reference will be made later. As above intimated, the para'inic oil is selected on the basis of its solvent capacity for the relatively low boiling hydrocarbons contained in the furfural-rich stream and therefore preferably consists essentially of relatively high molecular weight paralinic oil boiling substantially above the fractions to be removed. Advantageously, the initialboiling'point of the parafnic oil fraction is not -less` than 580 F. and preferably is at least 620 F. The parainic oil may be, for example, a solvent rened neutral oil of viscosity between 80/ 100 F. to 150/100c F. seconds, Saybolt Universal. Also, a raflinate from luid catalytic cracking unit decanter oil with an ASTM initial boiling point of at least 580 F. and preferably at least 620 F. as above indicated is effective. Its cetane number is preferably above about 55 (calculated) reflecting a minimum aromatic content which is obviously desirable to avoid contamination of the solvent with soluble hydrocarbons boiling above the boiling point of the solvent.

The tower 25 may operate with approximately 0.5- 3.0 volumes of parainic oil to one volume of recovered furfural. The temperatures of the entering streams are regulated so that the temperatures in the tower are in the range of about 90-140 F. Under these conditions, the phase accumulating in the bottom of the tower is composed of furfural of reduced light aromatic oil content. Extraction of a furfural-rich condensate as above containing about 25% of light aromatic oils results in delivery at the bottom of tower 25 of a solvent stream containing not more than about 4% of light aromatics having the boiling point and gravity range above indicated. The lean solvent stream passes from the bottom of tower 25 through pipe 30 to a solvent accumulator 31 from which it is cycled to pipe 12 previously mentioned supplying the charge oil extraction tower.

The extract phase of paraflinic oil containing dissolved light hydrocarbon fractions is drawn off from the top of the tower 25 through pipe 32 for water washing to recover any small amounts of dissolved furfural. Water washing is eected in tower 34 by passing the stream of oil upwardly against a down-flow of wash water introduced from any suitable source, not indicated, through pipe 35.

The oil-rich condensate of the stripped rainate oil and extract may be water washed simultaneously with the heavy oil in line 32, by continuously drawing off the oil layer through pipe 37 and combining it with the stream in pipe 32 entering the water wash tower 34.

Using furfural as the solvent, the water washing of the furfural from the rich parain oil may be effected with approximately 2-3 volumes of water per volume of oil at a temperature of about -l50 F.

The water washed oil is withdrawn from the top of tower 34 through pipe 40 and heater 41 from which it enters stripping tower 42 operated to strip out the light hydrocarbon fractions and regenerate the heavy parafnic oil for the extraction of additional furfural-rich layer. Therefore, in tower 42 the stripping may be effected with open steam at atmospheric pressure and introduced from any suitable source, not shown, through pipe 43. Under these conditions, the oil withdrawn from the bottom of the tower is a stripped parainic high molecular weight fraction which passes through pipe 44 into surge drum 45 and thence to the furfural extraction and purification tower 25. The overhead from the stripping tower 42 comprising the stripped light hydrocarbon fractions and steam passes through pipe 47 and condenser 48 to decanter 49 from which water is withdrawn as at 50 and light aromatic product hydrocarbons are recovered through pipe 51. The high molecular weight paratlinic oil may be originally introduced from any suitable source not disclosed through pipe 26, entering pipe 27 as shown.

Reverting again to the wash tower 34, the wash water containing thus recovered solvent is advantageously drawn 0H from the bottom of the tower through pipe 53 and combined with thewater-rich layer from the decanter 23 which is withdrawn through pipe 54. These combined water-rich streams, which, however, contain recoverable amounts of solvent, pass through 55 into a -solvent recovery fractionater 58.

The fractionater 58 operates to distill off from. the residual water an overhead azeotrope which passes through pipe 60 and condenser 61 to decanter 62 where separation of the condensate takes place to form a lower solvent-rich layer and an upper water-rich layer. The water-rich layer cycles continuously through pipe 63 to the inlet of the fractionater 58, whereas the solvent-rich layer is drawn off continuously through pipe 64 into the solvent accumulator 31. The residual water is continuously discharged as bottoms from fractionator 58, through pipe 59.

Accordingly, the solvent continuously recycling to the primary charge oil extract tower 11 is maintained at a desirably low or insignificant concentration of oil. I'herefore, the primary extraction is materially improved as regards the selective solvent capacity of the solvent for hydrocarbons, particularly light aromatic hydrocarbons.

For example, extraction of the foregoing charge oil with furfural containing 25% of an aromatic fraction, as above, requires 55% net furfural, on the basis of the charge oil'treated, to obtain a 70% rainate yield of 54 Cetane number. In contrast, extraction of the same oil with urfural containing 4% of the aromatic fraction requires only net furfural, on the same basis, to refine to the same cetane number with an equal yield of 70% ranate.

It will be understood that the temperatures, solvent dosages, etc., previously mentioned, may vary somewhat depending upon the nature of the feed oil, the degree of extraction desired, and the nature of the solvent employed. Moreover, the drawing is merely indicative of the apparatus and equipment used and no attempt has been made to detail heaters, exchangers, boilers, pumps, and other conventional equipment. For example, the fractionating columns may be provided with reboiler sections or other conventional means for facilitating fractionation or stripping. In general, the invention has application to the treatment of hydrocarbon mixtures having an A. S. T. M. boiling range of about 350 to 700 F.

It is contemplated recovering from the furfural dissolved oils having a boiling range of about 170 to 450 F. Therefore, a solvent paraflinic scrubbing oil having a high selectivity for these fractions is contemplated.

The invention is particularly concerned with the extraction of the feed oil by relatively high boiling organic solvent liquids which are miscible, at least to some extent, with water and with which constituents with the oil feed may form azeotropes. Selective solvents other than furfural may be used. They may include other derivatives of the furan group and other aldehydes, such as benz-aldehyde, ketones, furfuryl alcohol, tetra-hydro furfuryl alcohol, phenol-water solutions, etc.

As above intimated, it is contemplated ordinarily using a wet solvent, that is a solvent such as furfural, associated with varying amounts of Water depending upon the solvent rniscibility of the charge oil employed. In general, as is known, water tends to decrease the solvent capacity of the solvent for paraiiins and increase its selectivity for aromatics. Therefore, for the more miscible charge stocks, the water concentration is usually higher than for the less rniscible stocks which preferably employ a somewhat drier solvent. The invention is also applicable to the use of dry solvent, where indicated, but in any event the factors governing water addition rate, being known, and forming, per se, no part of the present invention, are subject to judgment of the skilled operator in light of the present disclosure.

Obviously, many modifications and variations of the invention as set forth may be made without departing from the spirit and scope thereof, therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

l. In the solvent rening of a feed oil containing coboiling aromatic constituents soluble in a liquid selective solvent and having true boiling points in the range of the solvent boiling temperature and below, wherein the feed oil is subjected to contact in a charge oil extraction zone with the solvent to form extract and rainate phases which are separately removed from the extraction zone and distilled to yield a distillate of solvent vapor containing said co-boiling oil constituents, leaving liquid product residues of oil substantially free of solvent, the improvement which comprises condensing such distillate, settling said condensate to form a solvent-rich liquid phase, contacting said solvent-rich liquid phase in a liquid-liquid extraction step with a relatively high molecular weight, high boiling paraiinic oil having an A. S. T. M. initial boiling point not lower than 580 F. effective to selectively dissolve from the said solvent-rich phase co-boiling aromatic constituents having a boiling point in the vicinity of the boiling point of said solvent and below, thereby producing a solvent-rich liquid having a reduced amount of said co-boiling constituents dissolved therein, Withdrawing the resulting solvent-rich liquid and recycling said withdrawn solvent liquid to said charge oil extraction zone.

2. The method according to claim 1 wherein said paranic treating oil has an initial boiling point of not less than 620 F.

3. The method according to claim 1 wherein said relatively high molecular weight parainic oil from the treatment of the solvent-rich phase is regenerated by stripping said aromatic constituents therefrom, and thereafter continuously recycled for the treatment of additional solvent-rich phase.

4. The method according to claim l wherein said relatively high molecular weight, high boiling paraiiinic oil rich in dissolved said co-boiling aromatic constituents is regenerated by water washing to recover contained solvent, and is thereafter stripped of said co-boiling aromatic constituents and recycled continuously for the treatment of additional solvent-rich phase.

5. In the solvent reluing of petroleum oil containing co-boiling aromatic hydrocarbons soluble in liquid furfural and having true boiling points in the range ot' the boiling point of furfural and below, wherein the charge oil is subjected to liquid-liquid Contact in the charge oil extraction zone with furfural to form extract and rainate phases which are separately removed from the extraction zone and distilled to yield a distillate containing furfural and said co-boiling hydrocarbons, leaving liquid product residues of oil substantially free from furfural, the improvement which comprises condensing such distillate, settling the resulting condensate to produce a furfuralrich liquid phase containing said co-boiling aromatic hydrocarbons dissolved therein, contacting said furfuralrich liquid phase in a liquid-liquid extraction step with a relatively high molecular weight, high boiling paratlinic oil having an A. S. T. M. initial boiling point not lower than 580 F. effective to selectively dissolve from said furfural-rich liquid phase the co-boiling aromatic hydrocarbons contained therein having a boiling point in the vicinity of the boiling point of furfural and below thereby Substantially decreasing the aromatic hydrocarbon content of the furfural-rich liquid phase, withdrawing the resulting furfu1'al-rich liquid phase and recycling the resulting withdrawn furfural-rich phase to said charge oil extraction zone.

References Cited in the iile of this patent UNITED STATES PATENTS 2,216,933 Atkins, Jr. Oct. S, 1940 2,305,038 Schumacher Dec. l2, 1942 2,472,499 Stone June 7, 1949 2,475,147 Manley Iuly 5, 1949 2,497,588 Davies Feb. 14, 1950 

1. IN THE SOLVENT REFINING OF A FEED OIL CONTAINING COBOILING AROMATIC CONSTITUENTS SOLUBLE IN A LIQUID SELECTIVE SOLVENT AND HAVING TRUE BOILING POINTS IN THE RANGE OF THE SOLVENT BOILING TEMPERATURE AND BELOW, WHEREIN THE FEED OIL IS SUBJECTED TO CONTACT IN A CHARGE OIL EXTRACTION ZONE WITH THE SOLVENT TO FORM EXTRACT AND RAFFINATE PHASES WHICH ARE SEPARATELY REMOVED FROM THE EXTRACTION ZONE AND DISTILLED TO YIELD A DISTILLATE OF SOLVENT VAPOR CONTAINING SAID CO-BOILING OIL CONSTITUENTS, LEAVING LIQUID PRODUCT RESIDUES OF OIL SUBSTANTIALLY FREE OF SOLVENT, THE IMPROVEMENT WHICH COMPRISES CONDENSING SUCH DISTILLATE SETTLING SAID CONDENSATE TO FORM A SOLVENT-RICH LIQUID PHASE, CONTACTING SAID SOLVENT-RICH LIQUID PHASE IN A LIQUID-LIQUID EXTRACTION STEP WITH A RELATIVELY HIGH MOLECULAR WEIGHT, HIGH BOILING PARAFFINIC OIL HAVING AN A. S. T. M. INITIAL BOILING POINT NOT LOWER THAN 580* F. EFFECTIVE TO SELECTIVELY DISSOLVE FROM THE SAID SOLVENT-RICH PHASE CO-BOILING AROMATIC CONSTITUENTS HAVING A BOILING POINT IN THE VICINITY OF THE BOILING POINT OF SAID SOLVENT AND BELOW, THEREBY PRODUCING A SOLVENT-RICH LIQUID HAVING A REDUCED AMOUNT OF SAID CO-BOILING CONSTITUENTS DISSOLVED THEREIN WITHDRAWING THE RESULTING SOLVENT-RICH LIQUID AND RECYCLING SAID WITHDRAWN SOLVENT LIQUID TO SAID CHARGE OIL EXTRACTION ZONE. 